An electronic apparatus such as a laser printer has a paper feed roller (i.e., driven unit) coupled with a motor and disposed inside a main unit casing, and this motor drives the paper feed roller to rotate and deliver paper to a predetermined position.
The above motor comprises a stator including a stator core having a plurality of magnetic poles disposed at first predetermined intervals along the outer periphery thereof, and a rotor disposed around the outer periphery of the stator. The rotor has a structure comprising magnets disposed at second predetermined intervals along the inner periphery thereof with their poles magnetized alternately to have different polarities.
The stator core is provided with an extended portion formed on each of the magnetic poles in a manner to extend from the base of the magnetic pole into a direction generally parallel to the magnet for improvement of a driving efficiency.
That is, the magnets are made larger in width (i.e., the width in a direction orthogonal to the circumferential direction) than a width at the base of the magnetic poles of the stator core in the same direction in order to bring the magnets as close as possible to a magnetic sensing element for magnetically sensing rotation of the rotor. It is for this reason that the conventional motor comprises the extended portions called end plates extended from the base of the magnetic poles of the stator core into the direction generally parallel to the magnets. These extended portions increase confronting areas between the magnetic poles of the stator core and the magnets to attain a high driving efficiency.
There are some techniques known to compose the stator core, of which one example is to stack a plurality of sheet-like plates each having nibs and dimples, and integrate them into one unit by swaging the nibs and the dimples between layers of the stacked plates. Also disclosed is a technique designed to improve a fastening strength among side plates having extended portions on both sides and inner plates between the side plates by means of connecting holes formed to extend through a laminated part in a direction of the rotational axis and bent tabs provided on the side plates, wherein the bent tabs are fitted into the connecting holes to fasten together the side plates and the laminated part. Such a technique is disclosed in patent literature 1, for example.
In the process of forming the magnetic poles having the extended portions, the fastening strength can be increased among the side plates and the inner plates, as described above, by fitting the bent tabs provided on the side plates into the connecting holes formed in the laminated part.
However, the magnetic poles discussed above have the structure designed to use the bent tabs provided on the side plates to fasten them to the laminated part. The bent tabs are therefore prone to troubles such as becoming broken and deformed in the processes of fabrication and transportation. There is also another problem attributed to pointed ends of the bent tabs, which make handling of the side plates difficult. In addition, the above structure is likely to lower the manufacturing efficiency due to its use of two different fastening methods, i.e., the nib-and-dimple swaging of the sheet-like plates to form the laminated part, and the press-fitting by using the bent tabs to fasten the laminated part and the side plates.    Patent Literature 1: Japanese Patent Unexamined Publication, No. 2007-215282